Sealants and adhesives play an important role in helping patients recover from surgery or trauma. Sealants and adhesives are useful in treating patients suffering from a variety of in vivo (e.g., internal) or topical conditions, including lacerations, tears, wounds, ulcers, astamoses, and surgical procedures. Sealants or adhesives can generally be used in any indication or application for which a suture or staple is presently used, and the sealant or adhesive often provides a better outcome than a suture or staple. Sealants or adhesives can also be applied more quickly to the injury site and often provide a better seal over the wound and healing. Various medicinal applications for sealants and adhesives are described below.
Skin Lacerations
Skin lacerations are tears in the skin produced by accidents, trauma, or as a result of a surgical procedure. Lacerations often require treatment in order to close the hole in the skin, stop bleeding, and prevent infection. Minor lacerations in the skin may be treated using an adhesive tissue to cover the wound. However, larger lacerations often require sutures or a glue to help seal the wound. For example, it is generally recommended that sutures or a glue be used to treat lacerations deeper than 0.25 inches having a jagged edge or loose flap of tissue. The location of the laceration may also affect the form of treatment. For example, it is advantageous to treat a skin laceration on a joint using a glue because adhesive tissue tends to limit mobility of the joint. The use of sutures or glues to treat skin lacerations can also reduce the chance of scar formation.
Liver Lacerations
Lacerations of the liver can occur from trauma or as a result of a surgical procedure. The liver is a highly vascularized organ and bleeds profusely when lacerated or traumatized. Liver lacerations are difficult to repair owing to the nature of liver tissue. Liver tissue has very weak cohesive strength, and, consequently, sutures and staples are not satisfactory because they may pull through the liver tissue. The lack of satisfactory wound treatment methods for liver lacerations combined with the fact that it is difficult to reach the veins that feed the liver renders liver lacerations particularly serious. In fact, severe lacerations of the liver often result in the patient's death due to bleeding. Thus, new materials to treat liver lacerations are needed.
Lung Surgery
The sealants and methods of the present invention are useful in lung surgery. Types of lung surgery include lobectomy, lung biopsy, lung-tissue removal, pneumonectomy, thoracoscopy, and thoracotomy. Risks associated with lung surgery include wound infection; post-surgical internal bleeding; air leaks through the lung wall; pain or numbness at the incision site; and inflammation of the lungs (pneumonia). Further, air leakage is frequently observed after thoracic procedures, such as pulmonary resection and decortication. It is important to create an air-tight seal so as to prevent or reduce severe complications, such as bronchopleural fistulas and infection resulting from extended chest tube drainage, extended recovery time, and postoperative morbidity related to pulmonary surgery. The sealants and methods of the invention should decrease or eliminate some of the problematic aspects of lung surgery, such as treatment of pneumothorax and pulmonary leaks.
Cornea—Corneal Lacerations/Perforations
Corneal perforations are produced by a variety of medical conditions (e.g., infection, inflammation, xerosis, neurotrophication, and degeneration) and traumas (chemical, thermal, surgical, and penetrating). Unfortunately, corneal perforations often lead to loss of vision and a decrease in an individual's quality of life. Depending on the type and the origin of the perforation, different treatments may be effective, ranging from suturing the wound to a cornea graft. However, the surgical procedures are difficult given the delicate composition of the cornea and the severity of the wound which increase the likelihood for leakage and severe astigmatism after surgery. In certain cases, for example, perforations that cannot be treated by standard suture procedures, tissue adhesives (glues) are used to repair the wound. This type of treatment is very attractive because the method is simple, quick and safe, and corresponds to the requirement of a quick restoration of the integrity of the globe, avoiding further complications. Besides an easy and fast application on the wound, the characteristics of an adhesive include: 1) bind to the tissue (necrosed or not, very often wet) with an adequate adhesion force; 2) be non-toxic; 3) be biodegradable or resorbable; 4) be sterilizable; and 5) not interfere with the healing process.
Various alkyl-cyanoacrylates are available for the repair of small perforations. However, these “super glues” present major inconveniences. Their monomers, in particular those with short alkyl chains, can be toxic, in part due to their ability to produce formaldehyde in situ. They also polymerize too quickly leading to applications that might be difficult and, once polymerized, the surface of the glue is rough and hard which leads to patient discomfort and a need to wear contact lens. Even though cyanoacrylate is tolerated as a corneal sealant, a number of complications have been reported including cataract formation, corneal infiltration, glaucoma, giant papillary conjunctivitis, and symblepharon formation. Furthermore, in more than 60% of the patients, additional surgical intervention is needed.
Other glues have also been developed. Adhesive hemostats, based on fibrin, are usually constituted of fibrinogen, thrombin and factor XIII. Systems with fibrinogen and photosensitizers activated with light are also being tested. If adhesive hemostats have intrinsic properties which meet the requirements for a tissue adhesive, then autologous products (time consuming in an emergency) or severe treatments before clinical use are needed to avoid any contamination to the patient. An ideal sealant for corneal perforations should 1) not impair normal vision, 2) quickly restore the intraocular pressure (IOP), 3) maintain the structural integrity of the eye, 4) promote healing, 5) adhere to moist tissue surfaces, 6) possess solute diffusion properties which are molecular weight dependent and favorable for normal cornea function, 7) possess rheological properties that allow for controlled placement of the polymer on the wound, and 8) polymerize under mild conditions.
The use of sutures has limitations and drawbacks. First, suture placement itself inflicts trauma to corneal tissues, especially when multiple passes are needed. Secondly, although suture material has improved, sutures such as 10-0 nylon (which is the suture of choice in the cornea and elsewhere) can act as a nidus for infection and incite corneal inflammation and vascularization. With persistent inflammation and vascularization, the propensity for corneal scarring increases. Thirdly, corneal suturing often yields uneven healing and resultant regular and irregular astigmatism. Postoperatively, sutures are also prone to becoming loose and/or broken and require additional attention for prompt removal. Finally, effective suturing necessitates an acquired technical skill that can vary widely from surgeon to surgeon and can also involve prolonged operative time.
Cornea—Corneal Transplants
During a corneal transplant or penetrating keratoplasty surgery the diseased cornea is removed with a special round cutting tool called a trephine. The donor cornea is cut to a matching size. Then, the donor cornea is placed upon the eye and secured in place with approximately 16 sutures around the transplant to secure the new cornea in place. A sutureless procedure would be highly desirable because sutures are associated with the following drawbacks and others: (1) sutures provide a site for infection, (2) the sutured cornea takes 3 months to heal before the sutures need to be removed, and (3) the strain applied to the new cornea tissue from the sutures can distort the cornea. An ocular adhesive may also serve as an adjuvant to sutures and/or reduce the necessary number of sutures.
Cornea—Clear Corneal Incision
Clear corneal incisions in the temporal cornea offer several advantages with phacoemulsification. The major advantage associated with phacoemulsification is the reduction in size of the entrance wound. Smaller wounds require fewer sutures or even no sutures at all, minimizing induction of astigmatism, decreasing bleeding and subconjunctival hemorrhage, and speeding the recovery of visual acuity. See Agapitos, P. J. Curr. Opin. Ophthalmol. 1993, 4, 39-43 and Lyle, W. A.; Jin, G. J. J. Cataract Refract. Surg. 1996, 22, 1456-1460. Surgeons typically examine the clear corneal incisions at the completion of the procedure by inflating the anterior chamber with balanced salt solution and applying pressure to the anterior cornea to check for leakage from the wound. If there is some leakage, the wound may be hydrated with balanced saline solution to seal fully the wound. This is done by injecting balanced saline solution into the open stromal edges. Hydration forces the two edges of the wound together, creating a tight seal. The endothelial cell pump can then remove the fluid from both the anterior and posterior portions of the wound, further sealing the wound together. See Fine, I. H. J. Cataract Refract. Surg. 1991, 17 (Suppl), 672-676. These tests for fluid flow, however, make several assumptions, including that the eye will remain well pressurized during the early postoperative period, that the hydrated wound will not be rapidly deturgesced by the corneal endothelium, and that the absence of aqueous outflow from the wound correlates with the inability of surface fluid from the tear film to flow into the wound, possibly contaminating the aqueous humor and predisposing to infection. However, intraocular pressure is known to vary in the postoperative period, frequently dropping to less than 5 mm Hg, and telemetric intraocular pressure monitoring devices suggest that large fluctuations in intraocular pressure occur in individual eyes in response to blinking. See Shingleton, B. J.; Wadhwani, R. A.; O'Donoghue, M. W.; Baylus, S.; Hoey, H. J. Cataract Refract. Surg. 2001, 27, 524-527 and Percicot, C. L.; Schnell, C. R.; Debon, C.; Hariton, C. J. Pharmacol. Toxicol. Methods 1996, 36, 223-228.
In a recent study, optical coherence tomography (OCT) confirmed the morphology of clear corneal incision wounds was not constant but varied in response to changes in the intraocular pressure. See McDonnell, P. J.; Taban, M.; Sarayba, M.; Rao, B.; Zhang, J.; Schiffman, R.; Chen, Z. P. Ophthalmology 2003, 110, 2342-2348. When the eyes were well pressurized (20 mm Hg or higher), the chambers were deeply formed, and the wound edges were well apposed. Elevation of intraocular pressure up to 40 to 50 mm Hg did not result in any separation of the wound edges. As the intraocular pressure was reduced to 10 mm Hg and below, the wound edges progressively separated. The separation began at the internal aspect of the wound, with posterior migration of the posterior and peripheral wound leaflet. This separation resulted in a wedge-shaped gaping in the internal aspect of the incision. Coincident with this wound margin separation, the spontaneous flow of aqueous humor through the wound was observed, and the chamber became shallower. Elevating the intraocular pressure resulted in prompt closure of the corneal wound at its superficial margin, termination of fluid leakage from the wound, and deepening of the anterior chamber. India ink was also applied to the surface of the cornea and quickly became visible through the operating microscope within the clear corneal incisions. Histologic examination of the wounds confirmed partial penetration of India ink particles along the edges of the incisions in every cornea. These studies demonstrated that a transient reduction of intraocular pressure might result in poor wound apposition in clear corneal incisions, with the potential for fluid flow across the cornea and into the anterior chamber, with the attendant risk of endophthalmitis. See McDonnell, P. J.; Taban, M.; Sarayba, M.; Rao, B.; Zhang, J.; Schiffman, R.; Chen, Z. P. Ophthalmology 2003, 110, 2342-2348.
Nonetheless, a progressive increase in the percentage of surgeons preferring self-sealing clear corneal incisions over scleral tunnel incisions in the United States and Europe has occurred over the past decade. See Learning, D. V. J. Cataract Refract. Surg. 1995, 21, 378-385 and Leaming, D. V. J. Cataract Refract. Surg. 2001, 27, 948-955. Some studies, however, reveal an increased incidence of postoperative endophthalmitis after clear corneal cataract incisions and a recent, retrospective, case-controlled study, reported that clear corneal incisions were a statistically significant risk factor for acute post-cataract surgery endophthalmitis when compared with scleral tunnel incisions. See John, M. E.; Noblitt, R. Endophthalmitis. Scleral tunnel vs. clear corneal incision; Slack, Inc.: Thorofare, N J, 2001; Colleaux, K. M.; Hamilton, W. K. Can. J. Ophthalmol. 2000, 35, 373-378; Nagaki, Y.; Hayasaka, S.; Kadoi, C.; Matsumoto, M.; Yanagisawa, S.; Watanabe, K.; Watanabe, K.; Hayasaka, Y.; Ikeda, N.; Sato, S.; Kataoka, Y.; Togashi, M.; Abe, T. J. Cataract. Refract. Surg. 2003, 29, 20-26; Stonecipher, K. G.; Parmley, V. C.; Jensen, H.; Rowsey, J. J. Arch. Ophthalmol. 1991, 109, 1562-1563; Lertsumitkul, S.; Myers, P. C.; O'Rourke, M. T.; Chandra, J. Clin. Exp. Ophthalmol. 2001, 29, 400-405; and Blake, A. C.; Holekamp, N. M.; Bohigian, G.; Thompson, P. A. Am. J. Ophthalmol. 2003, 136, 300-305. The visual outcome following severe endophthalmitis is always guarded. In a Western Australian Endophthalmitis Study more than half of the subjects suffered visual impairment, with 41% poorer than 20/200, 53% poorer than 20/125, and 58% poorer than 20/40. See Semmens, J. B.; Li, J.; Morlet, N.; Ng, J. Clin. Exp. Ophthalmol. 2003, 31, 213-219. Post-cataract endophthalmitis remains a potentially blinding complication of a sight-restoring procedure.
Refractive Surgery—Laser-Assisted In Situ Keratomileusis (LASIK)
Laser-assisted in situ keratomileusis is the popular refractive surgical procedure where a thin, hinged corneal flap is created by a microkeratome blade. This flap is then moved aside to allow an excimer laser beam to ablate the corneal stromal tissue with extreme precision for the correction of myopia (near-sightedness) and astigmatism. At the conclusion of the procedure, the flap is repositioned and allowed to heal. However, with trauma, this flap can become dislocated prior to healing, resulting in flap striae (folds) and severe visual loss. When this complication occurs, treatment involves prompt replacement of the flap and flap suturing. The use of sutures has limitations and drawbacks as discussed above. These novel adhesives could also play a useful role in the treatment of LASIK flap dislocations and striae (folds). These visually debilitating flap complications are seen not uncommonly following the popular procedure LASIK, and are currently treated by flap repositioning and suturing (which require considerable operative time and technical skill). A tissue adhesive could provide a more effective means to secure the flap.
Refractive Surgery—Lens Replacement
Cataracts or other diseases or injuries that lead to poorly functioning or damaged lens require the natural lens to be replaced. The optical properties of the normal eye lens are the consequence of a high concentration of proteins called “crystallins” forming a natural hydrogel. In vertebrate lenses, a range of differently sized protein assemblies, the alpha-, beta- and gamma-crystallins, are found creating a medium of high refractive index. The anatomical basis of accommodation includes the lens substance, lens capsule, zonular fibers, ciliary muscle and the elastic part of the choroid. Accommodation occurs through accurately controlled adjustments in the shape and thickness of the lens. The capsular bag is essential in transmitting the various extralenticular forces to the lens substance.
Modern cataract surgery can be done through a small incision (usually 2.5-3.5 mm). Once the incision is made, the anterior chamber is filled with a viscoelastic and the capsular bag is pricked with a needle. From this incision, a small continuous circular capsulorhexis (CCC) approximately 1.5 mm in diameter is performed using capsulorhexis forceps. Next endocapsular phacoemulsification is performed and the lens epithelial cells are removed by aspiration.
The normal function of the lens is to focus light onto the retina. Since removing the cataract leaves the eye without a lens to focus light, an artificial (intraocular) lens is commonly placed inside the eye. Most intraocular lenses are made of plastic, silicone, or acrylic compounds; have no moving parts; and last for the remainder of a person's life. These intraocular lens implants are held in place by the posterior capsule are not able to provide ocular accommodation. Refilling the lens capsule with in situ crosslinking materials described herein offers the potential to produce a synthetic hydrogel with mechanical properties similar to the lens of a twenty year old.
As such, the invention describes materials that reproduce the properties of the natural lens and these synthetic hydrogels maintain the integrity of the capsule to gain partial or full accommodation and restore vision to the patient. Alternatively, the dendritic polymers of the invention are incorporated in current IOL materials, such as PMMA, to alter hydrophilicity, water transport, refractive index, mechanical properties or biological response.
Retina—Retinal Holes
Techniques commonly used for the treatment of retinal holes, such as cryotherapy, diathermy and photocoagulation, are unsuccessful in the case of complicated retinal detachment, mainly because of the delay in the application and the weak strength of the chorioretinal adhesion. Cyanoacrylate retinopexy has been used in special cases. It has also been demonstrated that the chorioretinal adhesion is stronger and lasts longer than the earlier techniques. As noted previously with regard to corneal perforation treatment, the extremely rapid polymerization of cyanoacrylate glues (for example, risk of adhesion of the injector to the retina), the difficulty to use them in aqueous conditions and the toxicity are inconveniences and risks associated with this method. The polymerization can be slowed down by adding iophendylate to the monomers but still the reaction occurs in two to three seconds. Risks of retinal tear at the edge of the treated hole can also be observed because of the hardness of cyanoacrylate once polymerized.
Retina—Vitrectomy/Sclerotomy Incisions
The vitreous is a normally clear, gel-like substance that fills the center of the eye. It makes up approximately ⅔ of the eye's volume, giving it form and shape before birth. Certain problems affecting the back of the eye may require a vitrectomy, or surgical removal of the vitreous. During a vitrectomy, the surgeon creates small incisions/punctures in the eye (sclerotomies) for separate instruments. These incisions are placed in the pars plana of the eye, which is located just behind the iris but in front of the retina. The instruments which pass through these incisions include a light pipe, an infusion port, and the vitrectomy cutting device. Upon completion of pars plana vitrectomy, each sclerotomy site is closed with a single interrupted suture of 8-0 silk or 7-0 polyglycolic acid suture. After a vitrectomy, the eye is filled with fluid until the vitreous is replaced as the eye secretes aqueous and nutritive fluids.
Some of the most common eye conditions that require vitrectomy include 1) complications from diabetic retinopathy, such as retinal detachment or bleeding, 2) macular hole, 3) retinal detachment, 4) pre-retinal membrane fibrosis, 5) bleeding inside the eye (vitreous hemorrhage), 6) injury or infection, and 7) certain problems related to previous eye surgery.
Glaucoma—Filtering Bleb
Leaking filtering blebs after glaucoma surgery are difficult to manage and can lead to serious, vision-threatening complications. Filtering blebs can result in hypotony and shallowing of the anterior chamber, choroidal effusion, maculopathy, retinal, and choroidal folds, suprachoroidal hemorrhage, corneal decompensation, peripheral anterior synechiae, and cataract formation. A filtering bleb can also lead to the loss of bleb function and to the severe complications of endophthalmaitis. The incidence of bleb leaks increases with the use of antimetabolites. Bleb leaks in eyes treated with 5-fluorouracil or mitomycin C may occur in as many as 20 to 40% of patients. Bleb leaks in eyes treated with antimetabolities may be difficult to heal because of thin avascular tissue and because of abnormal fibrovascular response. If the leak persists despite the use of conservative management, a 9-0 to 10-0 nylon or absorbable suture on a tapered vascular needle can be used to close the conjunctival wound. In a thin-walled or avascular bleb, a suture may not be advisable because it could tear the tissue and cause a larger leak. Fibrin adhesives have been used to close bleb leaks. The adhesive is applied to conjunctival wound simultaneously with thrombin to form a fibrin clot at the application site. The operative field must be dry during the application because fibrin will not adhere to wet tissue. Cyanoacrylate glue may be used to close a conjuctival opening. To apply the glue, the surrounding tissue must be dried and a single drop of the cyanoacrylate is placed. The operative must be careful not to seal the applicator to the tissue or to seal surrounding tissue with glue given its quick reaction. A soft contact lens is then applied over the glue to decrease patient discomfort. However, this procedure can actually worsen the problem if the cyanoacrylate tears from the bleb and causes a larger wound.
Oculoplastics—Blepharoplasty Incisions
Blepharoplasty is an operation to remove excess skin, fat and muscle from around the eyes to correct droopy eyelids and bagginess under the eyes. It can be performed on the upper lids and lower lids, at the same time or separately. The operation may be done using either conventional or laser techniques. For surgery on the upper eyelids, cuts are made into the natural lines and creases in the lid, and into the laughter lines at the corner of the eye. For surgery on the lower eyelids, a cut is usually made just below the eyelashes. This means the scars run along the eye's natural folds, concealing them as much as possible. Excess fat, muscle and loose skin are removed, and the cut is closed using sutures. If only fat is being removed, sometimes the cut is made on the inside of the lower eyelid, leaving no visible scar. A tissue adhesive could provide a more effective means to secure the cuts made during surgery.
Gastrointestinal Anastomosis
The sealants and methods of the present invention should be useful in gastrointestinal anastomosis procedures. Gastrointestinal anastomosis is the technique of joining two pieces of bowel together. There are many techniques for gastro-intestinal anastomosis, including both mechanical stapled techniques and hand-sutured procedures. The technique may involve a simple end-end anastomosis of two pieces of jejunum, a more complex colo-anal anastomosis, or a biliary enteric join. One problem with techniques employing sutures or staples is that leakage may occur around the sutures or staples. See, for example, Bruce et al. Br. J. Surg. 88:1157-1168 (2001) reporting leakage rates of 5-8%. However, sealants and methods of the invention could be used to supplement the sutures or staples used in intestinal anastomoses, providing a better seal that reduces leakage. Compositions and procedures for proper sealing the consequences of a failed anastomosis are severe and frequently life-threatening. Although failures can be caused by myriad factors, including poor surgical technique (e.g., sutures that were not inserted correctly; knots that were tied too tightly rendering the ends ischaemic; or incorrect use of a staple gun), the sealants and methods of the invention should decrease or eliminate some of the causes of failed gastrointestinal anastomosis procedures.
Prostatectomy Urethral-Bladder Anastomosis
The sealants and methods of the present invention should be useful in prostatectomy urethral-bladder anastomosis procedures. Prostatectomy urethral-bladder anastomosis is the technique of joining together a patient's ureter and bladder after surgical removal of his prostate gland. Failures are caused by myriad factors, including poor surgical technique (e.g., sutures that were not inserted correctly; knots that were tied too tightly rendering the ends ischaemic). The sealants and methods of the invention should decrease or eliminate some of the causes of failed prostatectomy urethral-bladder anastomosis procedures.
Cartilage, Meniscus and Disk Repair
Cartilaginous tissues play important roles in contributing to load support and energy dissipation in the joints of the musculoskeletal system. These tissues include articular cartilage which is predominantly an avascular and alymphatic tissue with very low cell-density. As a result, articular cartilage has limited capacity for self-repair following injury or aging. Degeneration of cartilage in the meniscus, interverebral disks, or joints can lead to severe and debilitating pain in patients. Injuries to these tissues are often retained for many years and may eventually lead to more severe secondary damage. See Moskowitz, R. W., Osteoarthritis: diagnosis and medical/surgical management. 2nd ed.; W.B. Saunders Company: 1984. Today, more than one million knee, hip, and shoulder joint surgical procedures are performed annually in the United States as a consequence of trauma or a lifetime of wear and tear. See Praemer, A.; Furner, S.; Rice, D. P. Musculoskeletal Conditions in the United States, American Academy of Orthopaedic Surgeons: Rosemont, Ill., 1999. Despite the large number of patients suffering from cartilage degeneration, the only widely-available treatment options for cartilage degeneration are chronic administration of anti-inflammatory agents, total joint replacement, osteotomy, or allograft transplantation, each of which leads to mixed long-term results. The compositions and methods of the present invention should be useful in the treatment of such disorders and injuries.
Tissue Plane Applications
The materials of the invention can be applied to two planes of tissue and then these two tissues can be sealed together. Over time the sealant/hydrogel degrades as new tissue grows into the area. Applications include a number of cosmetic and tissue restoration surgeries. The sealant is used when the procedures involve significant tissue plane separation that may result in formation of seroma with associated complications, such as infection, e.g., general surgery procedures, such as mastectomies and lumpectomies, and plastic surgery procedures, such as abdominoplastys, rhytidectomy or rhinoplastys, mammaplasty and reconstruction, forehead lifts and buttocks lifts, as well as skin grafts, biopsy closure, cleft-palate reconstruction, hernia repair, lymph node resection, groin repair, Caesarean section, laparoscopic trocar repair, vaginal tear repair, and hand surgery.
Vascular and Cardiovascular Repair
The compositions and methods of the invention may be used for repairing, closing, and/or securing vascular and cardiovascular tissue. Representative procedures include coronary artery bypass grafts, coronary angioplasty, diagnostic cardia catheterization, carotid endarterectomy, and valve repair. An additional use of the sealant is for the repair of cardiac tissue after a myocardial infarction. The polymer would be applied to the infracted tissue to provide structural support to the weakened tissue. For example, the material would act as a sleeve for the cardiac tissue.
Repair of Dura Tissue
Dura tissue is a fibrous membrane covering the brain and the spinal cord and lining the inner surface of the skull. Standard methods of dural repair involve the application of interrupted sutures and the use of dural replacement materials (duraplasty). This is a meticulous surgery and suffers from the limitation that pinholes produced by surgical needles can cause leakage. Moreover, intraoperative dehydration can shrink the dura creating a difficult closure since it is difficult to approximate the edges with sutures. In older patients, the dura is often more susceptible to tearing when stretched and/or sutured because the dura can be thin and fragile. Adhesives such as fibrin have been explored for repair of dura tissue, but have had limited success. See “Glue in the Repair of Dural Defects in Craniofacial Resections,” J. Latyngology and Otology 106: 356-57 (1992); Kjaergard et al., “Autologous Fibrin Glue Preparation and Clinical Use in Thoracic Surgery,” Eur. J. Cardio-Thorc. Surg. 6: 52-54 (1992); Thompson et al., “Fibrin Glue: A Review of Its Preparation, Efficacy, and Adverse Effects as a Topical Hemostat,” Drug Intelligence and Clinical Pharmacy 22: 946-52 (1988); and Brennan, “Fibrin Glue,” Blood Reviews 5: 240-44 (1991). The sealants and methods of the present invention should be useful in repairing the dura after a craniotomy or laminectomy and prevent postoperative leakage of cerebrospinal fluid. See Preul et al. Neurosurgery 53:1189-1199 (2003) and Balance, C. A. in Some Points in the Surgery of the Brain and Its Membranes. London, Macmillan & Co.
Injection Site Wound
Many therapeutic agents are administered to a patient by injection. However, one complication of this procedure is that the tissue at the injection site can become infected or susceptible to poor healing. One clinical situation where infections are prone to occur is when a therapetic agent is injected into the eye of a patient. This mode of administration is used in the treatment of age-related macular degeneration (AMD) and results in about 2% of patients suffering from infection or endophthalmitis.
Age-related macular degeneration is a disease that blurs the sharp, central vision needed for “straight-ahead” activities such as reading and driving. Specifically, AMD is a progressive disease of the retina where the light-sensing cells in the central area of vision (the macula) stop working and eventually die. The disease is caused by a combination of genetic and environmental factors, and it is most common in people who are age sixty and over. In fact, AMD is the leading cause of visual impairment in the elderly population. It is estimated that fifteen million people in the United States have AMD, with approximately two million new cases diagnosed annually. There are two types of AMD-wet and dry. Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula. These new blood vessels tend to be very fragile and often leak blood and fluid. The blood and fluid raise the macula from its normal place at the back of the eye. Damage to the macula occurs rapidly and loss of central vision can occur quickly. On the other hand, dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye. Central vision is gradually lost. In this disease, Vascular Endothelial Growth Factor (VEGF) is a key growth factor, which promotes the new growth blood vessels. Currently, it is believed that that when the retinal pigment epithelial (RPE) cells begin to wither from lack of nutrition (i.e., ischemia), VEGF is up-regulated and new vessels are created. Yet, the vessels do not form properly and leaking results. This leakage causes scarring in the macula and eventual loss of central vision. To prevent or inhibit this neovascularization process, antiangiogenic drugs are given the patient. In most cases, the drugs are injected into the vitreous of the eyeball, then pass into the subretinal space where the vessels proliferate. These drugs include mucagenm squalamine lactate, combretastatin 4 prodrug, and avastin.
The sealants and methods of the present invention should be useful in sealing injection site wounds. Among the various possibilities, the injection can be given and then the sealant applied to the injection site, or alternatively the sealant can be applied and then the injection can be done through the sealant.
Therapeutic Use of Crosslinked Polyalkyleneimines
To date poly alkyleneimines (PAIs) have been used primarily as gene transfection agents with limited success. In general, large PAIs (25,000 molecular weight and higher) are more efficient at forming complexes and condensing with polynucleic acids, but their associated toxicity has also been reported to increase with increasing molecular weight. As a strategy to reduce this toxicity, polyalkylene glycols (PAGs), such as monomethoxy-polyethylene glycols, have been grafted to the PAIs in vitro before condensation with polynucleic acids. In a few cases, PAIs have been combined with difunctionally activated PEG in dilute solution to produce linear block copolymers of PAI and PAG, or in an emulsion polymerization process to produce small PAI/PAG microspheres. In both of these cases, the PAI/PAG block copolymers were synthesized in vitro for the purpose of condensing with polynucleic acids for gene transfection.